The THz region (1 THz=33 cm−1 or 4 meV) lies in the far infrared spectral range where conventional thermal sources are very weak. For example, a blackbody source at 2,000° K. provides less than 1 μW per cm−1 of spectral power density for a typical spectroscopy application. Whereas narrow band sources of such radiation have been available using free-electron laser (FEL) technology, significant advances in broadband THz sources have occurred over the past decade with the advent of coherent THz radiation emission from photocarriers in biased semiconductors. Table top systems using optical rectification of femtosecond lasers either at high repetition rates (Bonvalet, A., Joffre, M., Martin, J. L. and Migus, A., “Generation of ultrabroadband femtosecond pulses in the mid-infrared by optical rectification of 15 fs light pulses at 100 MD rate”, Appl. Phys. Lett. 67, 2907-2909 (1995)) or high peak power are now routinely available.
While such prior art systems are capable of producing THz radiation and even coherent THz radiation for very brief periods of time at high power or for prolonged periods at very low power, none of the prior art systems has been capable of producing a stable THz radiation at high power, i.e. above about 2 milliwatts for any significant period of time. The specific distinctions between such prior art systems and that of the present invention are described more fully below in connection with FIGS. 1 and 2 that form part of this application.